The investigation deals with the measurement of fetal and maternal placental capillary blood pressures, osmotic pressures and resistances to flow. It will further investigate the Frank-Starling mechanism of the fetal heart, and the regulation of fetal and maternal arterial blood pressures. Further investigations are designed to demonstrate the existence of fetal regulatory mechanisms, other than the well known cardiovascular mechanisms that occur in the adult also, that interact with the stabilization of fetal placental blood flow, since the ordinary regulation mechanisms can be shown not to be capable of regulating steady state fetal placental blood flow. The current year will focus on the membrane properties of the chorioallantoic placenta.